Atrial natriuretic peptide (ANP): response to NaCI is attenuated in rat atria in vitro after hypophysectomy

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Abstract
The present study documents the effects of hypophysectomy on the NaCl‐stimulated release and on the basal secretion rates of ANP from rat atria in vitro. Three weeks before the experiments rats were subjected to hypophysectomy or to a corresponding sham operation. Atria were excised and superfused in an organ bath with a physiological buffer solution (PBS, 294 mosmol kg‐1). After a control period of 5 min, superfusion was made with hyperosmotic NaCI (330 mosmol kg‐1) for 10 min, and then again with PBS, but now for 15 min. Atria were paced with field stimulation (4 Hz, 20 V, 1 ms) and the resting tension was kept at 5 mN. The sham‐operated animals responded with a significant increase (P < 0.05) in the secretion rate of ANP (from 137 ± 13 pg ml‐1 [n = 35] to 235 ± 24 [n = 34], means + SE) to the NaCI stimulus. The hypophysectomy blunted the ANP response to hyperosmotic NaCl. In addition, basal secretion rate was signficantly (P < 0.001) lower in the hypophysectomized than in the sham‐operated animals during the whole experiment. Gel filtrations revealed that, during the hyperosmotic NaCI, both groups secreted exclusively ANP 1–28. We conclude that hypophysectomy blunts the basal as well as stimulus‐induced in‐vitro release of ANP from rat atria.